Support is requested for a Keystone Symposia meeting entitled Gut Microbiota Modulation of Host Physiology: The Search for Mechanism, organized by Fredrik Backhed, Ruth E. Ley and Yasmine Belkaid. The meeting will be held in Keystone, Colorado from March 1-6, 2015. Over the past decade, it has become evident that the gut microbiome is an important environmental factor that affects many physiologic processes, such as cell proliferation and differentiation, behavior, immune function, and metabolism. Moreover, it may contribute to a wide variety of diseases, including cancer, inflammatory diseases, metabolic diseases, and responses to pathogens. In this regard, this meeting will emphasize mechanistic understandings of the relationship between microbiota and host physiology, rather than simply characterize microbiota in different disease states. Speakers will address not only bacteria in the gut, but also fungi and microbiome on the skin and in the lung. The goal of this meeting is to facilitate the understanding by which mechanisms of the microbiota modulate host physiologic processes and increase our understanding on how an altered microbiota contributes to health and disease in humans. In addition, the broad representation of speakers from diverse fields, such as microbiology, immunology, physiology, and infectious disease, is likely to foster new collaborations. The meeting's focus on digestive diseases, including nutrition, and associated diabetes, such as obesity and diabetes, make it highly relevant to NIDKK's mission.